1. Field of the Invention
The present invention relates to an organic light emitting diode and a method of fabricating the same. More particularly, the present invention relates to an organic light emitting diode, and a method of fabricating the same, that is configured to reduce or eliminate gases entrapped between an organic layer and an underlying layer when the organic layer is formed.
2. Discussion of Related Art
organic light emitting diode may include organic layers as part of the device structure. For example, in forming an organic light emitting diode such as an organic light emitting diode, a lower electrode, e.g., an anode electrode, and/or a pixel-defining layer may have a thin organic layer formed thereon. The organic layer may be, e.g., a hole injection layer, a hole transport layer, an emission layer, a hole blocking layer, an electron transport layer, an electron injection layer, etc. Additional layers such as an upper electrode, e.g., a cathode electrode, may then be formed on the organic layer.
A variety of methods have been developed to form organic layers in organic light emitting diodes. Such methods include, e.g., deposition and lithographic methods. The deposition method may involve forming an organic layer by vacuum-depositing an organic material using a shadow mask. However, it may be difficult to form a high resolution pattern, e.g., one with a very fine pitch, using such a method, and applying the deposition method to large-area display devices may also be difficult.
Lithographic methods may involve depositing an organic material, followed by patterning the material using a photoresist to form the organic layer. Such lithographic methods may be suitable for forming high-resolution patterns. However, some of the pattern-forming steps of the lithographic method, e.g., etching, developing with a developing solution, etc., may cause the organic layer to deteriorate.
In order to avoid the difficulties associated with the deposition and lithographic methods, an ink jet method may be employed to directly pattern the organic layer. In the ink jet method, a solution containing an organic material is discharged from a head of an ink-jet printer to form the organic layer. The solution may include the organic material dissolved or dispersed in a solvent. The ink jet method has the advantage of being relatively simple. However, it may not produce organic layers of uniform thickness, yields may be low and it may be difficult to apply large-area display devices.
A thermal transfer method has been proposed to form organic layers in organic light emitting diodes and it may offer advantages over the methods described above. The thermal transfer method may form an organic layer using, e.g., laser-induced thermal transfer, wherein the organic material is provided on a donor substrate, the donor substrate is placed in close contact with the device substrate, and a laser is scanned across the donor substrate. Heat energy provided by the laser causes the organic material to transfer to the donor substrate, forming the organic layer.
The thermal transfer method may be applied to form, e.g., an organic-processible hole transfer layer, such as an underarray of an organic light emitting diode, red, green and blue organic layers, etc. Laser-induced thermal transfer may offer various advantages, such as formation of high-resolution patterns, uniformity of film thickness, an ability to laminate multiple layers, extensibility into a large motherglass, etc., which make it suitable for the manufacture of large-scale organic light emitting diodes. Such a laser-induced thermal transfer may be used for fabricating a color filter for a liquid crystal display device, forming a pattern of luminescent materials, etc.
FIG. 1 illustrates a plan view of a stage in a conventional method of fabricating a pixel unit of an organic light emitting diode, and FIG. 2 illustrates a cross-sectional view of a stage in a conventional method of fabricating a pixel unit of an organic light emitting diode, taken along a line A-A′ of FIG. 1.
Referring to FIGS. 1 and 2, a thin-film transistor 107 and a first electrode layer 209 may be formed on a substrate 200. The thin-film transistor 107 may include a buffer layer 201 and a semiconductor layer 102 that has an active channel layer 102a and ohmic contact layers 102b. A gate insulating layer 203 and a gate electrode 204 may be formed on the active channel layer 102a and the ohmic contact layers 102b. An interlayer dielectric 205 may cover the gate electrode 204 and the gate insulating layer 203, and may have electrode contacts 106a and 106b penetrating therethrough. A planarization layer 208 may overlie these features, and an electrode layer 209 may be formed on top of the planarization layer 208. The electrode layer 209 may make contact with the electrode contact 106a through a via hole 202. A pixel-defining layer 100 may be formed on the planarizing layer 208 and the electrode layer 209, and may have an opening 114 formed therein to expose part of the electrode layer 209.
An organic layer 101, which may be, e.g., a light emitting region, may be formed in the opening 114 of the pixel-defining layer 100 using, e.g., laser-induced thermal transfer. The organic layer 101 may extend laterally beyond the opening 114, so as to be disposed on the electrode layer 209 and on the pixel-defining layer 100. The pixel-defining layer 100 may extend laterally beyond the organic layer 101 along the circumference of the organic layer 101. Thermal transfer of the organic layer may be achieved by scanning a laser lengthwise along the organic layer 101, i.e., in the downward direction illustrated in FIG. 1.
Referring to FIG. 2, a thermal transfer donor film 216 may include a light-to-heat conversion layer 214 formed on a base substrate 213, and may include an organic material-containing transfer layer disposed on the light-to-heat conversion layer 214. The donor film 216 may further include an interlayer 215 between the light-to-heat conversion layer 214 and the transfer layer.
The donor film 216 may be arranged adjacent to and facing an upper portion of a pixel-defining layer 100. A laser may be-irradiated onto and scanned across the donor film 216, such that the light-to-heat conversion layer 214 converts the laser light into heat. The transfer layer may melt and separate from the donor film 216 so as to form the organic layer 101 on the pixel-defining layer 100.
As the transfer layer is transferred from the donor film 216 to the pixel-defining layer 100, gases may be entrapped. In particular, gases may be trapped between the organic layer 101 and the pixel-defining layer 100 and/or the electrode layer 209.
The gas entrapment may be more significant in the last region of interface between the organic layer 101 and the pixel-defining layer 100 and/or electrode layer 209, i.e., the final region scanned by the laser. For example, referring to FIG. 1, gases may be entrapped near the lower region of the organic layer 101 when the laser is scanned from the upper region toward the lower region. As a result, adhesion between the organic layer 101 and the pixel-defining layer 100 and/or the electrode layer 209 may be unsatisfactory, due to the entrapped gases.